The present invention relates to a circuit for a semiconductor device, and more particularly to a substrate voltage generator included inside the semiconductor device.
Recently, as the integration density of the semiconductor device increases, the size of transistors becomes more minute, thereby degrading the reliability on the supply voltage and increasing the power consumption. Thus, most semiconductor devices include a substrate voltage generator to stabilize the threshold voltage of MOS (Metal Oxide Semiconductor) Transistor, to reduce junction capacitances, and to prevent parasitic transistors and incorrect operations due to the undershoot of external TTL (Transistor-Transistor Logic) gates. There are two methods for the generation of substrate: one is controlling the pumping by detecting the substrate voltage if it is far from a predetermined value, and the other is controlling the pumping capacitance by detecting the level of RAS(Row Address Strobe) signals.
However, the conventional substrate voltage generator is degraded at high temperature, thereby resulting in the unstability of the substrate voltage. Particularly, in the case of CMOS (Complementary MOS) circuits, the latch-up characteristics are apt to be weakened. This degradation is mainly caused by an oscillator in the substrate voltage generator. That is, as the temperature increases, the oscillation frequency of the oscillator decreases, thereby varying the substrate voltage. Also, as the semiconductor device becomes smaller, the driving capacity of the substrate voltage generator is lowered so that the incorrect operation occurs easily and the reliability is degraded.